Employing the facultative photoheterotrophic bacterium, Rhodopseudomonas sphaeroides, we hope to understand those genetic, physiologic and biochemical events which are involved in the localized intracellular differentiation, induced by anaerobiosis, of the cytoplasmic membrane resulting in the formation of a physically contiguous but structurally and functionally new membrane system (ICM). We further hope to understand how the cell maintains this differentiated state by an in vitro analysis of those events which direct newly synthesized proteins to either the cytoplasmic membrane, the ICM or to both. Similarly, we hope to understand the maintenance of the structural and functional integrity of the ICM by investigating: 1. the role of phospholipid exchange proteins and phospholipid biosynthetic activities in the movement of phospholipids from their site of synthesis to the ICM at precisely pre-determined times in the cellcycle, 2. the role of lipid structure and/or protein structure in the maintenance of the structural and functional isolation of the ICM, 3. the functional dependency of the ICM on the structural relationships of its interacting components through the use of specific cross-linking reagents, immunological, electron microscopic analyses and detailed biochemical and physiological studies of isolated functional components from wild type and mutant organisms. Finally, we shall investigate using immunochemical, molecular genetic, biochemical and physiological techniques the fate of the ICM and its components when growing cells are returned to conditions which no longer favor the maintenance of the ICM. The application of specific genetic probes will facilitate these studies by permitting us to investigate the transcriptional regulation of ICM development and maintenance effected by O2 as well as adjustments in the intracellular levels and composition of the ICM effected by light intensity. A thorough understanding of membrane structure, function, and synthesis is essential to an understanding of the secretory, energetic, conductance and selective permeability properties of membranes observed in normal and diseased tissue.